add a macro to wrap a privilegied function

src/lxc/caps.h

@@ -22,7 +22,34 @@
  */
 #ifndef _caps_h
 #define _caps_h
-int lxc_caps_down(void);
-int lxc_caps_up(void);
-int lxc_caps_init(void);
+
+extern int lxc_caps_down(void);
+extern int lxc_caps_up(void);
+extern int lxc_caps_init(void);
+
+#define lxc_priv(__lxc_function)			\
+	({						\
+		int __ret, __ret2, __errno = 0;		\
+		__ret = lxc_caps_up();			\
+		if (__ret)				\
+			goto __out;			\
+		__ret = __lxc_function;			\
+		if (__ret)				\
+			__errno = errno;		\
+		__ret2 = lxc_caps_down();		\
+	__out:	__ret ? errno = __errno,__ret : __ret2;	\
+	})
+
+#define lxc_unpriv(__lxc_function)		\
+	({						\
+		int __ret, __ret2, __errno = 0;		\
+		__ret = lxc_caps_down();		\
+		if (__ret)				\
+			goto __out;			\
+		__ret = __lxc_function;			\
+		if (__ret)				\
+			__errno = errno;		\
+		__ret2 = lxc_caps_up();			\
+	__out:	__ret ? errno = __errno,__ret : __ret2;	\
+	})
 #endif